1. Field of Invention
THIS INVENTION relates to directional drilling equipment and more particularly to directional drilling equipment utilised for forming generally horizontal passages in the ground, (usually 1 to 10 meters from the surface) for electrical or telephone cables, gas or water pipes, etc. Such directional drilling equipment is known per se. The drilling equipment is directional in the sense that the drill can be, in effect, steered to allow it to be navigated along streets or roads, for example, or under roads and rivers, without striking the foundations of buildings or water mains, gas mains or sewers.
2. Description of Related Art
Such systems are known and utilise, for example, a drill bit which is not rotationally symmetrical about its axis and/or has asymmetrically disposed fluid flushing outlets, so that material can be removed preferentially from one side of the bore being drilled whereby, in use, the end of the bore being drilled can deliberately be made to drift to one side or the other of the axis of the regions of the bore further from the end whereby the drill can be xe2x80x9csteeredxe2x80x9d. WO97/49889 discloses one example of a directional drilling arrangement. The primary mechanism for deviation in known directional drilling equipment is the out-of-balance transverse force component acting on the drill bit, and hence the drill string, caused where there is no rotation of the drill string and the bit is being forced into the medium being drilled. There is some additional nonsymmetric flushing causing preferential removal of debris from one side of the bore-hole which can also assist deviation in certain softer formations.
This transverse force component effectively causes deviation or steering of the drill and drill string in the particular azimuth direction required when the drill string is not rotating. When uniform rotation is recommenced, there is no further effective transverse force component and the drill string continues along a new straight axis (which is then a different axis from the previous one). This operation can be carried out fairly frequently to effect the desired rate of change of direction, or steering.
In conventional drilling equipment, the drilling bit has a splined shank which is received in the correspondingly splined end of an endmost tubular element (or chuck) of the drilling string, the cooperating splines preventing relative rotation between the drill bit and the chuck. Normally manufacturing techniques and convenience dictate that in such known arrangements, the arrangement of splines on the drill bit shank and the chuck is rotationally symmetrical.
According to one aspect of the invention, there is provided drilling apparatus including a drill string terminating in a drill chuck and a drill bit detachably fitted in the drill chuck, the drill bit having a shank received in the drill chuck, the drill chuck and the drill bit shank having cooperating spleens thereon and the distribution of the said splines about the axis of the drill chuck and bit being irregular so that the drill bit can be fitted in the drill chuck in only one orientation.
Preferably the drill string incorporates a pneumatically operable hammer arranged to apply axial impact forces to the drill bit, the apparatus including first passageways for supplying compressed air to such hammer mechanism and separate second passages for applying fluid to the drill bit.
In the last-noted arrangement, separate air exhaust ports and drilling fluid discharge ports are provided on the bit.
According to yet another aspect of the invention there is provided drilling apparatus including a drill string terminating in a drill chuck and a drill bit detachably fitted in the drill chuck, the drill bit having a shank received in the drill chuck, the drill bit shank having a first splined region adjacent a head position of the drill bit and having splines cooperating with grooves between splines of an internally splined complementary portion of said chuck wherein the drill bit has a second splined region adjacent its rear end and has a spline-free band located between said first and second splined regions, and the apparatus includes a liner, adjoining the chuck and having an internal axial passage which is splined in correspondence with the second splined region, over an axial extent less than that of said spline-free band, the axial passage in said liner having, immediately behind the splined region of the liner, a region which is free of splines and has an internal diameter greater than the external diameter of the second splined region of the drill bit shank, said liner being rotatable between an angular position in which the splines thereon are in axial alignment with those in the second splined region of the chuck and an angular position in which they are out of such alignment, whereby the drill shank can be inserted in the passages of complementary cross section in the chuck and the liner, with the splines of the chuck and liner aligned with the corresponding splines of the drill bit shank, until said second splined region of the drill bit shank is within the splineless region of the liner and the end splined region of the liner is within the spline-free band of the drill bit shank, and the liner thereafter rotated so as to move its splines out of axial alignment with those of said second splined region of the drill shank, thereby preventing axial removal of the drill bit.
According to yet another aspect of the invention there is provided drilling apparatus comprising a series of elongate sections releasably interconnected end to end by interengaging screw threads, orienting means for ensuring that a first component carried by a first said section adopts a predetermined orientation with respect to a second component carried by, or forming part of, an adjoining second said section when the first and second section are screwed together, wherein said first component is rotatable with respect to said first section and wherein the first section carries a member, herein referred to for convenience as an azimuth member, which is rotatable with respect to said first section but is non-rotatable with respect to said first component, and wherein the second section carries a reference member which is fixed against rotation relative to said second component and is engageable with said azimuth member in a predetermined angular orientation relative to the azimuth member as said first and second sections are screwed together end to end, and wherein, when so engaged relative rotation about the axis of said sections, between said azimuth member and said reference member is precluded by such engagement, and wherein one of said azimuth member and said reference member is resiliently displaceable away from the other as said first and second section are screwed together, whereby during an initial phase of screwing said first and second sections together the resiliently displaced member can be displaced axially, to counteract the progressive approach of said first and second sections, as the latter are screwed together, whilst rotating relative to the other said member, until said predetermined angular orientation of the reference member with respect to the azimuth member is reached, allowing the azimuth member and reference member to engage and thereby prevent further relative rotation between the two, whereby the azimuth member, and said first member coupled thereto, will maintain said predetermined orientation relative to said second component despite further rotational movement between said first and second section during completion of the screwing together of said first and second sections.
According to a still further aspect of the invention there is provided percussion drilling bit operable when accorded only a limited range of angular movement about a longitudinal axis of the bit, and wherein the bit comprises cutting tips or inserts arranged in a series of rings or tiers concentric with said longitudinal axis, such that for a predetermined angle of rotation of the bit about said axis, the zone of action of each cutting tip or insert in each said ring or tier overlaps that of at least the adjoining cutting tips or inserts in the same ring or tier.
In the preferred embodiments of the invention, a sensing and transmitting apparatus is incorporated in the drill string, adjacent to the drill chuck, to sense and transmit to the surface information about the position and orientation of the drill bit or other drilling equipment. This apparatus can relay back to the surface readings of depth, position and angular position of the drill string. This information, inter alia, allows the angular position of the drill bit to be determined and allows the bit to be positioned at the required angle for steering in the desired direction. Sensing and transmitting apparatus capable of operating as described above is herein referred to, for convenience, as a xe2x80x9csondexe2x80x9d or as a data transmitter
Preferably the sonde is mounted in the drill string via a resilient suspension arrangement to isolate the sonde from mechanical shocks.